1. Field of the Invention
The present invention relates to a marking apparatus for marking a surface, especially for making a position mark on a wall or ceiling of a building to be worked on.
2. Prior Art
Numerous devices and methods for projecting a light marking, especially with the help of lasers, are known. A device is described in U.S. Pat. No. 4,448,528, with whose aid a measured position on a floor of a room can be projected exactly vertically to a ceiling above it. However a mark projected, in this manner is not immediately usable as a reference for working the concerned surface, because it is generally not possible to position a work tool according to the projected mark, without covering the projecting beam at the same time. A pen must therefore by used to apply a permanent ink mark at the position of the projected mark, or a tip of a small object, such as a nail, must be held on the projected mark and struck with a hammer in order to make a mark in the form of a small hole.
This procedure however frequently produces inaccurate results, since a person who makes the permanent mark can only observe the pen or tip of the object that is used to make the mark at an angle to the projected beam, so as not to cover it, so that parallax errors can easily occur. Moreover the places to be marked, especially on a high ceiling of a, room, are reached only with difficulty, which understandably increases the cost of the work performed.
According to the invention means for making a mark on a surface, including a writing instrument such as a stylus, are combined with a light-sensitive device to form a common marking unit. The marking apparatus also includes a control means, which puts the light-sensitive device and the means for making the mark on the surface in an operational relationship, whereby the means for making the mark is operated to make the mark when the light-sensitive device detects a light signal. The marking apparatus according to the invention need only be held against the surface to be marked and it will automatically make a mark on that surface when it meets the projected beam, in contrast to the additional effort required to make the mark with the aid of a pen or with a hammer and nail.
The writing instrument is preferably provided with a nozzle, which is controlled by the control device to deliver ink powder or paint, so that the mark is applied to the surface.
The light-sensitive device is preferably a position-resolving arrangement of individual light sensors, especially a linear arrangement of light sensors, such as photo diodes, and the control device is equipped to control the means for making the mark so that it places the mark at a position on the surface, which corresponds to a position at which the light-sensitive device detects the projected light beam. An extended arrangement of light sensors of this sort is obviously easier to position in a projected light beam than an individual light sensor. The control by the control circuit occurs according to the geometric properties of the marking unit, so that the mark is placed at a position on the surface at which -the projected light beam would impinge or meet the surface if the marking unit itself were not on the surface.
Especially when the means for making the mark includes an individual writing tool or stylus the control circuit is preferably equipped in order to move the stylus according to a position where the light-sensitive device detects the light signal, so that the stylus can put the mark at the position on the surface indicated with the projected beam.
Preferably the means for making the mark and the light-sensitive device are mounted on opposite sides of a frame of the marking unit. This frame can be placed before the surface to be marked so that the means for making the mark is on the side of the frame facing or closest to the surface and the light-sensitive device is mounted on the opposite side of the frame facing or closest to the source of the projected light beam.
In many applications, especially on transferring a mark from the floor to the ceiling of a room or on projecting a horizontal line on the wall of a room, the projected beam is substantially perpendicular to the surface to be marked. Under these conditions a parallax-free application of the mark is possible, when the control device controls the means for making the mark, so that the position where it places the mark and the position at which the light-sensitive device detects the light signal are arranged on a vertical line, which extends from the side of the frame on which the means for making the mark is mounted to the position on the surface to be marked.
In order to simplify the transfer to a continuous mark such as a line onto a surface, the frame of the marking tool is provided with wheels for moving.its housing over the surface to be marked. Preferably the frame has three wheels in order to guarantee a definite stable position of the marking tool on the surface even when the surface is rough.
According to a preferred embodiment of the invention at least one of these wheels can be steered or controlled, for example by a person who operates the marking tool or by the control circuit according to the location where the light-sensitive device detects the light signal, in.order to be able to rapidly and conveniently move it along a line extending on the surface and defined by the projected light beam, without the light-sensitive.device wandering away from the projected beam.
For use in inaccessible locations the marking apparatus is preferably also equipped with a stud or projection for a pole, with whose help, for example, an operator on the floor of a room can press the tool against the ceiling.